Conventional methods for measuring cognitive load, include:                subjective measures, such as self-rating scales;        physiological techniques, such as pupil dilatation, heart rate and galvanic skin responses;        task or performance based measures, such as critical error rates and task completion times; and        behavioural measures, such as speech disfluencies, self-talk etc.        
There are a number of problems with these methods for measuring cognitive load, including:                some of the methods are intrusive and disrupt the normal flow of performing the task;        some of the methods are physically uncomfortable for the user;        cannot be conducted in real-time as they are too labour-intensive;        the data quality is potentially unreliable outside laboratory conditions; and        the data quality can be affected by outside factors, such as user's stress level.        
Objectively quantifying cognitive load that can be applied uniformly across fields as a standard, or to allow comparison between subjects remains an open problem. In fact, historically, the most consistent results for cognitive load assessments have been achieved through self-rating subjective measures. These allow users to describe in fine detail their perceived level of cognitive load induced by various types of task.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.